Intoxication by Xanthium cavanillesii in cattle and sheep in southern Brazil.

Three outbreaks of Xanthium cavanillesii intoxication occurred in the spring in the State of Rio Grande do Sul, southern Brazil. All outbreaks were observed in paddocks with sandy soils in flood plains along water streams. The paddocks had been under water, and after water withdrawal cattle were introduced to those areas which had seedlings of X cavanillesii and shortage of other forage. Mortality varied between 3 and 58%. Most animals were found dead or died a few hours after observation of clinical signs. The main lesion was a swollen liver with acute diffuse centrilobular necrosis. The disease was produced experimentally by feeding cotyledons at 0.75 and 1% bw in calves, and at 1.5 and 2% bw in sheep. Clinical signs and gross and microscopic lesions were similar to those observed in field cases. X cavanillesii in the 4-leaf stage with the attached cotyledons was also toxic for cattle and sheep, but the same plant without cotyledons lost its liver toxicity. The lethal dose of cotyledons divided in 5 daily doses was not toxic for cattle and sheep, demonstrating the non-cumulative effect of the plant.